1. Field of the Invention
The present invention relates to an objective lens actuator for recording or reproducing optically in a disk-shaped recording and reproducing medium.
2. Prior Art
Recently, the apparatus for recording and reproducing information (called an optical disk apparatus) by using a disk-shaped optical recording and reproducing media (called a disk) is widely used in recording of sound, picture, and data as its benefits of large capacity and high speed operation are recognized. Among the components incorporated in the optical disk apparatus, the objective lens actuator is regarded as an important mechanical part that determines the recording and reproducing performance.
A conventional objective lens actuator is described below while referring to related drawings. FIG. 13 is a perspective outline view of a conventional objective lens actuator, FIG. 14 is a perspective exploded view of the objective lens actuator, and FIG. 23 is a partial sectional view showing a mounting part of an electromagnetic coil of the same. This example shows an objective lens actuator using four linear spring members for holding a lens holding member, and is widely used at the present.
In FIG. 13 and FIG. 14, in a lens holding member 32, an objective lens 1 is adhered to the upper surface in the drawing, a balance weight 34 is adhered to the lower surface, soldering substrates 35 for soldering and fixing front ends of linear spring members 39 are adhered to both sides, and two magnets 3 magnetized in the N-S direction are adhered to the other sides as shown in the drawing. At one end on a base 40, a support holder 37 is fixed, and soldering substrate 38 for soldering the other ends of the linear spring members 39 are adhered to the support holder 37. The linear spring members 39 have been cut to specified length, and four members are arranged parallel through a tiny hole 43 of the soldering substrate 38 made of printed circuit board, a tiny hole 44 of the support holder 37, and a tiny hole 45 of the lens holding member 32, and the both ends are soldered at soldering parts 41 and 42 in the drawing in the soldering substrate 35 fixed to the lens holding member 32 and the soldering substrate 38 fixed to the support holder 37.
Oppositely across a clearance to the magnets 3, electromagnetic coils 36 for driving them electromagnetically are fixed at specified positions similarly on the base 40 through printed circuit boards 47 as shown in FIG. 23, and more specifically a winding 36b having an axis in arrow X1-X2, and a winding 36c having an axis in arrow Y1-Y2 are wound around a coil frame 36a, and leaders of beginning and end of these windings are wound around roots 36e of metal pins 36d planted on the coil frame 36a, and are soldered 36f. The pins 36d of this coil frame 36a are inserted into four holes 47a of the printed circuit board 47, and are fixed by soldering 47c, and are electrically connected to the print pattern. Mounting holes 47b of the printed circuit board 47 are fastened with screws to screw holes 40a of the base 40 as shown in FIG. 14 through spacers 48, and are drawn out by lead wires, not shown, soldered to the print pattern, and are connected to an electric circuit which is not shown. From above this assembly, a cover 46 having an opening 46a is put on the base 40 through a hook part 46b.
Referring now to FIG. 19, the structure of the root for supporting the four linear spring members 39 of the support holders 37 in FIG. 13 is explained. The peripheral parts not related with the description are not shown in the drawing. In FIG. 19, seeing the support holder 37 from the lens holding member 32 side, four holes 37d are formed in the root for supporting the linear spring members 39, and a viscoelastic material, such as silicone gel, is injected into the holes 37d as brake members 37e.
In thus constituted conventional objective lens actuator, the operation is described below. By the linear spring members 39 disposed parallel to each other, the lens holding member 32 is supported at one side on the support holder 37, so that the lens holding member 32 can be moved parallel in the direction of arrow X1-X2 and arrow Y1-Y2. When a current is passed in two windings having the axis in arrow X1-X2 of the electromagnetic coil 36 and axis in arrow Y1-Y2, a driving force in the directions of arrow X1-X2 and arrow Y1-Y2 is generated in the magnets 3 by the electromagnetic force generated between the magnets 3 magnetized in the N-S direction oppositely across a clearance, thereby driving the lens holding member 32, hence the objective lens 1 fixed thereon, in the directions of arrow X1-X2 and Y1-Y2.
Accordingly, through the objective lens 1, the focal point of the laser light focused on a disk, not shown, above the objective lens can be moved, and information signals are recorded or reproduced, following the runout in the disk surface and eccentricity in the radial direction.
Supposing to pass a constant current regardless of the frequency to the winding having an axis in arrow X1-X2 of the electromagnetic coil 36, the state of the lens holding member 32 supported by one side on the linear spring members 39 by the electromagnetic force acting between the magnetic field generated by this current and the magnets 3 in the direction of arrow X1-X2 is shown in the lens system driving frequency characteristic in FIG. 18 in which the axis of abscissas denotes the frequency (Hz) of the driving current of the electromagnetic coil 36 and the axis of ordinates is the lens amplitude (dB). In the diagram, a primary resonance point f1 appears usually around scores of hertz (about 30 to 50 Hz). If the vibration system balance is poor and the linear spring members 39 are distorted, a torsional vibration on the axis of the linear spring members 39 is caused in the lens holding member 32, and an unnecessary resonance appears around a double frequency, slightly above f1, as indicated by broken line, in FIG. 18. The primary resonance is attenuated usually by braking the linear spring members 39. As an example of this method, as shown in FIG. 19, a brake member composed of viscoelastic material is injected into the peripheral holes 37d of the linear sprig members 39 of the fixed supporting holder 37 of the linear spring members 39, or, although not shown, a tube made of viscoelastic material is put around the linear spring members 39, but these measures are not effective to suppress the undesired resonance or secondary resonance point f2 appearing at higher frequency.